1. Field of the Invention
The present invention relates to a hydraulic master cylinder for vehicle adapted to hydraulically actuate brakes and clutches of automobiles and two- and three-wheeled automotive vehicles, and more particularly to a hydraulic master cylinder in which an opening at one end of a cylinder main body which is made to open at both ends thereof is closed with a lid member so as to form a cylinder bore.
The present invention relates to a hydraulic master cylinder for vehicle adapted to hydraulically actuate brakes and clutches of automobiles.
2. Description of the Related Art
Among conventional hydraulic master cylinder for vehicle, there is a hydraulic master cylinder for vehicle in which a lid member is mounted in an opening at one end of a cylinder main body which is made to open at both ends thereof so as to form a cylinder bore. For example, in a plunger hydraulic master cylinder, a lid member is mounted in an opening at one end of a cylinder main body, and a piston guide is mounted in an interior of the cylinder main body, whereby a cylinder bore is formed therein. A primary piston and a secondary piston are inserted into the cylinder bore, and a primary hydraulic chamber and a secondary hydraulic chamber are defined between the two pistons and between the secondary piston and the lid member, respectively.
The lid member includes a cylindrical portion and a flange portion which are formed integrally, the cylindrical portion being adapted to be inserted into the cylinder main body and the flange portion being adapted to cover one end portion of the cylinder main body. A threaded portion is provided on an outer circumference of a distal end of the cylindrical portion and on an inner circumference of the cylinder main body, respectively, and an output port which communicates with a discharge port in the cylinder main body is formed rearward of the threaded portions. A seal ring is fitted on the distal end of the cylindrical portion and near the flange portion, and by screwing the distal end of the cylindrical portion into the cylinder main body, the lid member is mounted in the cylinder main body (for example, refer to JP-UM-B-8-2002 Pages 1 to 2, FIG. 1).
In the aforesaid hydraulic master cylinder for vehicle, however, in mounting the lid member in the cylinder main body, since the seal ring is screwed into the cylinder main body while being revolved, the seal ring is twisted, which may lead to a risk that the durability is deteriorated.
In addition, when a hydraulic pressure is generated in the secondary hydraulic pressure chamber, the seal ring provided near the flange portion is subjected to a hydraulic pressure from a working fluid which has oozed out into a gap between a flange side of the lid member which is not in threaded engagement with the cylinder bore and the cylinder bore. Due to this, there needs to provide at the distal end of the cylindrical portion a sufficient length of threaded portion which is threaded into the cylinder bore so as to prevent the dislocation of the lid member from the cylinder bore.
Furthermore, in mounting and dismounting the lid member in and from the cylinder bore, while a tool hole is formed in a bottom wall of the lid member, dust and mud collect in the tool hole to clog it up therewith, this leading from time to time to a risk that a tool cannot be inserted into the tool hole so clogged.
In a plunger master cylinder which is one of master cylinders, an opening at one end of a through bore formed in a cylinder body is closed by a lid member so as to form a bottomed cylinder bore, a cylindrical piston guide is fitted into the cylinder bore, a piston is slidably inserted into the piston guide so that a hydraulic pressure chamber is defined between the piston and a bottom portion of the cylinder bore, a cup seal having an outer circumferential lip portion which resiliently contacts an inner wall of a cylinder bore, an inner circumferential lip portion which resiliently contacts an outer wall of a piston and a base portion which couples both the lip portions together at rear ends thereof is disposed within the cylinder bore with both the lip portions being made to face the hydraulic pressure chamber, and the cup seal is held by a piston guide which enters a recessed portion between the lip portions.
Working fluid supply holes which open communications between a reservoir and the hydraulic pressure chamber are formed in the piston guide and the piston, respectively, and in conjunction with the movement of the piston towards the hydraulic pressure chamber side, when the working fluid supply holes in the piston are closed by the cup seal, the communication between the hydraulic pressure chamber and the reservoir is cut off, and when the piston moves further towards the hydraulic pressure chamber, the pressure within the hydraulic pressure chamber is increased. As this occurs, both the lip portions of the cup seal increase their press contact forces against the inner wall of the cylinder bore and the outer wall of the piston, respectively, in association with the increased in pressure within the hydraulic pressure chamber. Then, when something like a negative pressure is generated within the hydraulic pressure chamber as the piston moves backwards, the working fluid on the reservoir side deflects both the lip portions of the cup seal, so that the working fluid is supplied into the hydraulic pressure chamber (for example, refer to JP-A-10-59161 Pages 2 to 6, FIGS. 1 to 9).
In the cup seal holding structure described above, however, since an outside of the inner circumferential lip portion is press held towards the outer wall of the piston, the resilient contact force of the inner circumferential lip portion against the piston outer wall is increased, and when the piston moves, there is caused a risk that the inner circumferential lip portion is bitten into the working fluid supply holes, and in addition, since the cup seal is press held only towards the outer wall of the piston, the cup seal moves in conjunction with the movement of the piston, and an ineffective stroke of the piston is increased.